Speaker system

Abstract: The speaker system of the invention comprises an acoustic tube with one end coupled to the back side of the speaker unit and the other end released to a sound field space through an opening window, and at least one air chamber is disposed on the way of the route of the acoustic tube, in which the sectional area of the air chamber is set larger than the sectional area of the acoustic tube, and the sectional area of the opening window is set smaller than the sectional area of the acoustic tube, and therefore the air chamber composes an acoustic filter so that the resonance frequency components of high degree in the acoustic tube may not be radiated from the opening window, and formation of peaks and bottoms of frequency characteristic due to interference with the sound radiated from the front side of the speaker is prevented. The opening window of a small sectional area lowers the resonance frequency of the acoustic tube. The speaker system of the invention according to an other embodiment, comprises an acoustic tube with one end coupled to the back side of the speaker unit and the other end released to a sound field space through an opening window, and at least one branch chamber; the branch chamber possessing different route lengths causes a phase difference in the acoustic tube to cancel the resonance in the acoustic tube, so that formation of peaks and bottoms in the frequency characteristic may be prevented.

Description: The present invention relates to means for enhancing the frequency characteristic and efficiency of a speaker system expanded in the bass register by coupling an acoustic tube to the back side of a speaker unit. A speaker system expanded in the bass register by coupling an acoustic tube to the back side of a speaker unit has been known so far. The conventional speaker system is described below-with reference to a drawing. Fig. 5 is a sectional view showing the constitution of a conventional speaker system. In the diagram, numeral 1 denotes a cabinet, 2a, 2b, 2c, 2d and 2e are partitions for composing an acoustic tube by partitioning the inside of the cabinet 1, 3 is an open window disposed in the lower part of a front panel of the cabinet 1, and 4 is a speaker unit disposed above the front panel. In this constitution, the operation is described below. The partitions 2a, 2b, 2c, 2d and 2e disposed in the cabinet 1 compose an acoustic tube in the cabinet 1, and the sound delivered from the back side of the speaker unit 4 is radiated from the open window 3 through the acoustic tube. The acoustic tube resonates at a specific determined frequency fn. Supposing the overall length of the acoustic tube to be L and the sound velocity in the air to be C, the resonance frequency fn is expressed as fn = (C/4L) x (n+1) where n is 0, 1, 2, or any other integer. In the case of n=0, that is, at the frequency resonating with 1/4 wavelength in the acoustic tube, the acoustically magnified sound is radiated from the open window 3 of the acoustic tube, and the efficiency is notably enhanced near the frequency at the reproduction limit of bass. At n=1, that is, at the frequency resonating with 1/2 wavelength in the acoustic tube, the sound is radiated from the front side of the speaker unit 4, while the sound from the back side is inverted in phase by delay of half wavelength in the acoustic tube, and is radiated from the open window 3. Both sounds added in the front space of the cabinet 1, so that the sound pressure level increases at that frequency. At n=2, that is, at the frequency resonating with 3/4 wavelength in the acoustic tube, same as in the case of n=0, the acoustically magnified sound is radiated from the open window 3. Thus, in the bass region, a speaker system of high efficiency has been realized. In such conventional constitution of speaker system, however, even at the frequency of medium and high frequency region corresponding to n=3 or higher, resonance occurs in the acoustic tube, and the sound is radiated from the open window 3. The sound from the open window 3 complicatedly interferes with the front sound of the speaker unit 4, and peaks and bottoms of sound pressure occur in the medium and high frequency region as indicated by broken line in the reproduced sound pressure frequency characteristic diagram in Fig. 2 The characteristic of the medium and high pressure region is extremely deteriorated, thereby lowering the sound quality. Besides, the frequency of the bass reproduction limit is defined by the overall length L of the acoustic tube, and therefore to reproduce the lower frequency region, the overall length L of the acoustic tube must be extended, which causes to increase the size of the speaker system. A speaker system having the features of the preamble of Claim 1 is known from Patent abstracts of Japan vol. 13, no. 285(E-780) 29 June 1989 & JP-A-10 068 99. Patent abstracts of Japan vol. 16, no. 475 (E-1273) 2 October 1992 & JP-A-41 070 298 describes an elongate speaker system with an open window having a smaller sectional area than the acoustic tube. It is a goal of the invention to solve the above problems, and to present a speaker system of high performance, capable of enhancing the radiation efficiency in the low frequency region, flat in the reproduced sound pressure frequency characteristic in the medium and high frequency region, and capable of lowering the frequency of the low frequency sound reproduction limit. This goal is achieved with the speaker system having the features of the characterizing part of claim 1. Preferable embodiments are the subject matter of the dependent claims. The speaker system of the invention operates as follows. The air chamber provided on the way of the acoustic tube acts as an acoustic filter by the reactance component presented by the acoustic compliance of the acoustic tube, and the sound of the medium and high frequency region from the back side of the speaker unit is acoustically cut off, and not released from the open window. The open window of smaller sectional area than the sectional area of the acoustic tube works as an acoustic mass. The resonance frequency of the acoustic tube is thus lowered, and the reproduction band is widened to a lower resonance frequency than the one determined by the overall length L of the acoustic tube, so that a speaker system of excellent frequency characteristic may be presented. Besides, the portion possessing at least two distinct routes with individually different route lengths generates a phase difference in the acoustic tube, cancels resonance and prevents occurrence of peaks and bottoms. Fig. 1 is a sectional view showing the constitution of a speaker system useful in understanding the invention. Fig. 2 is a graph showing the reproduction sound pressure frequency characteristic of the speaker system of Fig. 1 and a conventional speaker system. Fig. 3 is a sectional view showing the constitution of another speaker system useful in understanding the invention. Fig. 4 is a sectional view showing the constitution of a speaker system in an embodyment of the invention Fig. 5 is a conventional speaker system Fig. 1 is a sectional view of a speaker system useful in understanding the invention. In the drawing, numeral 5 denotes an acoustic tube, 6 is an air chamber functioning as an acoustic filter, being formed on the way of the route of the acoustic tube 5 so as to have a wider sectional area than the sectional area of the acoustic tube 5, 7 is a speaker unit coupled to the acoustic tube 5, and 8 is an open window functioning as an acoustic mass, possessing a smaller sectional area than the sectional area of the acoustic tube 5. This constitution comprises an acoustic tube 5 coupled to the back side of the speaker unit 7, the air chamber 6 functioning as an acoustic filter on the way of the acoustic tube 5, and the open window 8 functioning as an acoustic mass. In this constitution, the speaker system acts as follows. The compliance of the air chamber 6 works as capacitance component, and when the frequency of the sound passing through the air chamber 6 becomes higher, the impedance of the air chamber 6 becomes smaller, and attenuated components are radiated from the open window 8. In the low frequency region, on the other hand, the impedance presented by the air chamber 6 is large, and the acoustic tube 5 functions as in the prior art, and the low frequency component is directly radiated from the open window 8. Therefore, by setting the cross sectional area of the air chamber 6 for making the cut-off frequency of the air chamber 6 nearly equal to 3/4 of the resonance frequency of the acoustic tube 5, the air chamber 6 has no effect on the frequency component less than about the frequency expressed by fn = 3C/4L (n=2) intended to enhance the efficiency in the low frequency by making use of the resonance of the acoustic tube 5, and applies attenuation by filter effect for higher frequency components, and therefore the sound radiated from the open window 8 has a smaller interference with the sound radiated from the front side of the speaker unit 7 in the medium and high frequency region,so that a nearly flat reproduction sound pressure frequency characteristic is realized in the register from the low frequency region to the medium and high frequency region. Moreover, since the open window 8 having a smaller sectional area than the sectional area of the acoustic tube functions as an acoustic mass, the resonance frequency of the acoustic tube 5 can be set lower than the resonance frequency determined by the overall length (L). An example of characteristic of this speaker system is indicated by the solid line in Fig. 2. Thus, according to the speaker system of Fig. 1, an acoustic filter is composed by disposing an air chamber on the way of the route of the acoustic tube. The sectional area of the air chamber is set larger than the sectional area of the acoustic tube so that its cut-off frequency may be nearly equal to 3/4 of the resonance frequency of the acoustic tube, and therefore the interference of the front side sound of the speaker unit and the sound from the open window in the medium and high frequency is decreased to obtain a smooth frequency characteristic without peaks and bottoms. Moreover, by setting the sectional area of the opening window smaller than the sectional area of the acoustic tube, the bass register can be lowered below the frequency determined by the length of the acoustic tube, so that a speaker system of excellent characteristics can be realized. In this speaker system, the cross-section of the air chamber 6 is described to be square shaped, but the shape can also be different as far as the sectional area is not too large. Similar effects can be obtained regardless of the shape. Moreover, by disposing a plurality of air chambers, the characteristic of the acoustic filter may be set variously. A second speaker system useful in understanding the invention is described herein by reference to Fig. 3 which is a sectional view. The same constituent elements as in the speaker system of Fig. 1 are identified with same reference numerals, and their explanations are omitted. In the drawing, numeral 9 is a cabinet disposed at the front side of the speaker unit in order to form a space of an enclosed structure. Explaining the operation in this constitution, the acoustic tube 5 disposed at the back side of the speaker unit 7 improves the reproduction capacity in the low frequency region in the same way as in the speaker system according to Fig.1, and also makes smooth the reproduction sound pressure frequency characteristic in the medium and high frequency region. In this speaker system, furthermore, the cabinet 9 of enclosed structure is disposed at the front side of the speaker unit 7. Enclosing the air at the front side of the speaker is effective in suppressing the amplitude of the diaphragm of the speaker under the low frequency region reproduction limit, and the diaphragm does not vibrate abnormally if an excessive input is applied to the speaker unit. Generation of abnormal sound such as bottom beat phenomenon of speaker is prevented, so that a speaker system of high reliability and high resistance to input can be presented. The air chamber in this speaker system disposed along the acoustic tube does not prevent interference with the direct sound from the front side of the speaker unit, but prevents interference with the direct sound due to vibration of the cabinet itself even when enclosed, thereby offering the same effects as in the speaker system according to Fig. 1. In Fig. 3, the acoustic tube 5 is folded over only once, but the number of foldings is not limited, as a matter of course. Fig. 4 is a sectional view of the constitution of an embodiment of the invention. In the drawing, numeral 10 is a portion (branch chamber) disposed on the way of the route of the acoustic tube 5, and a part of the acoustic tube 5 is divided into a plurality of routes 10a, 10b differing in length. The other constituent elements are the same as in the speaker system according to Fig. 1 first embodiment and are identified with the same reference numerals, and detailed descriptions are omitted. In this constitution according to the invention, the speaker system of the embodiment functions as follows. The acoustic tube 5 coupled to the back side of the speaker unit 7, and the air chamber 6 disposed on the way present an excellent speaker system, excellent in low frequency region reproduction, and smooth in reproduction sound region characteristic in the medium and high frequency region, same as in the speaker system according to Fig. 1. A branch chamber 10 disposed on the way of the route of the acoustic tube 5 can cancel sharp peaks and bottoms due to resonance of the acoustic tube 5 by generating phase difference by routes 10a, 10b differing in length, so that an excellent speaker system widened in the reproduction frequency band can be presented. In addition, by selecting the difference in length of the routes 10a, 10b of the branch chamber 10, the frequency desired to be canceled can be selected, and it can be set freely as required. In this embodiment, the branch chamber 10 comprises two routes 10a, 10b, but the same effects are obtained by dividing into a plurality of more than two depending on the desired reproduction sound pressure frequency characteristic. Thus, according to the speaker system of the invention, by disposing the air chamber on the way of the acoustic tube to compose the acoustic filter, formation of peaks and bottoms due to resonance frequency of higher degree can be prevented, and by disposing branch chambers differing in the route length on the way of the acoustic tube, the resonance in the acoustic tube is canceled by generating phase difference, and formation of peaks and bottoms of frequency characteristic is prevented, so that a smooth frequency characteristic can be realized.

Claims: Speaker system comprising a speaker unit (7) and an acoustic tube (5), one end of said acoustic tube (5) being coupled to the backside of said speaker unit and the other end of said acoustic tube (5) being released to a sound field space through an open window (8), wherein at least one air chamber (6) is disposed in the acoustic tube (5), the sectional area of the air chamber (6) being larger than the sectional area of the acoustic tube (5), characterized by the sectional area of the open window (8) being smaller than the sectional area of the acoustic tube (5), said acoustic tube (5) presenting a portion (10) in the form of a chamber comprising at least two distinct routes (10a,10b) with individually different route lengths. Speaker system according to claim 1 characterized by said portion (10) comprising a plurality of distinct routes each providing individually different route lengths. Speaker system according to one of the claims 1 or 2, characterized by said speaker unit (7) being coupled with its front side to said sound field space. Speaker system according to one of claims 1 or 2, characterized by said speaker unit (7) being coupled with its front side to an enclosed space.

Inventors: HONDA KAZUKO, TAKAYAMA SATOSHI, HONDA, KAZUKO, TAKAYAMA, SATOSHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: H04R1
IPC codes: H04R1